Bernoulli’s Principle

This page will be dealing with Bernoulli’s Principle.  Before we get into that, however, I would like you to try a couple of things.  First, go into the bathroom and get a strip of toilet paper about 12 to 16 inches long.  Now, hold one end up to your chin so it looks like you have a ZZ Top beard.  Wait… you don”t know who ZZ top is?  I will wait while you watch this video:

Ahhhh yeahhh!  It doesn’t get any cooler than ZZ.  Now, as you were watching that video, I hope you were holding the toilet paper up to your chin so you looked just like them.  If not, I will wait while you watch the video again…

Ok.  Now.  With your ZZ TP Beards on, blow a stream of air like you are trying to blow out birthday candles.  What happens to the toilet paper?  Should be pretty cool. If nothing happens, try again.  The paper should lift magically into the air.  If you can’t get it to work, turn to one of your classmates that is smarter, more talented, and cooler than you for help.  What’s happening here?  It’s Bernoulli’s principle.  What’s Bernoulli’s principle?  Well, I am so glad you asked!

In fluid dynamics, Bernoulli’s principle states that for an inviscid flow of a nonconducting fluid, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid’s potential energy.

Ok.  So what in the heck does that mean?  First, we have to understand the words that were coming out of his mouth.  The first word that probably threw you was “inviscid,” which (if you remember your vocabulary unit on prefixes) you probably guessed means not viscid.  You were right.  Viscid, as I am sure you have known since you were 3 or 4 years old, means “having a glutinous or sticky properties.” So inviscid pretty much means free-flowing.

The important part of his principle is the INCREASE IN SPEED correlating with the DECREASE IN PRESSURE.  That’s why I typed it in yellow.  It was kind of a color-coded foreshadowing.  Bernoulli discovered an inverse relationship between the speed of fluid matter (like air and water) and its pressure.  As the speed increases, the pressure decreases.  And and the speed decreases, the pressure increases.  It is important to note that the pressure happens at a right angle to the moving matter.  Now, as you let that seep in, go find a bendy straw and  a ping pong ball.  Bring these items back here.  I’ll wait.

Ok.  Do you have them?  If so, skip the rest of this paragraph and scroll down to the next paragraph. If you didn’t get them, why not?!  This was not a difficult task! Bendy straws, and a ping pong ball!  Go do it and then scroll down to the next paragraph!

This next part is fun.  Bend the straw’s little elbow into a 90 degree angle and put the long part in your mouth so it looks like you are general Patton smoking his corn cob pipe.  What’s that you say?  You don’t know what Patton looks like?  he’s this guy:

What a sexy beast!!!  Anyway, put the straw in your mouth and blow a steady stream of air through the straw.  Hold the ping pong ball above the air stream and gently let it go.  The ball should levitate.  If it does not, turn to a friend that is smarter, more talented, and cooler than you for help. Got it now?  Did you make it magically levitate?  This is because the column of fast moving air has a relatively lower pressure than the stationary air surrounding it.  And because of the whole right angle thing, every molecule of air pushes directly inward on the ball holding it in place.

So cool!  Now for your actual assignment:  Answer the following 4 questions on a sheet of paper.  Please don’t write on here, as it will soil the computer screen.

1.  Draw a diagram illustrating Bernoulli’s principle as pertaining to the toilet paper beard.  Vector lines may be useful here.

2.  Draw a diagram illustrating what happened with the ping pong balls.  Once again, vector lines.

3.  You know when you take a shower and the tub has a shower curtain instead of glass doors?  You hop in and turn on the water and invariably the shower curtain sticks to your leg!  I hate that!  But why does it happen?  I’ll bet Bernoulli could tell us.  But he’s dead.  So can you explain it?

That’s it! You are done.  As a reward for your hard work, please relax and enjoy the following video: